Ethylene/Alpha-Olefin Copolymers for Better Optical and Mechanical Properties and Processability of Film Made Therefrom

ABSTRACT

A Ziegler-Natta catalyzed ethylene/alpha-olefins copolymer is provided having sporadic long chain branches and reversed comonomer composition distribution or short chain branching distribution (SCBD) in the high molecular weight fractions. According to the invention, polyethylene film made with the inventive copolymer has a balance of improved physical, optical, mechanical properties as well as processability. In one aspect, the film includes a 1% secant modulus of greater than 25,000 psi, a film haze of less than 10, a film clarity of greater than 90, a dart impart resistance of greater than 500 g/mil, and a MD tear strength of greater than 500 g/mil.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to polyethylene copolymers with sporadiclong chain branches and high molecular weight tail along with a reversedcomonomer distribution for improving processability, melt strength, andoptical properties, while maintaining excellent dart impact and tearstrengths. More specifically, the present invention relates to linearlow density polyethylene (LLDPE) with uniform compositions, which isobtainable by copolymerization of ethylene with C₃- to C₁₀-alpha-olefinsin the presence of a special Ziegler-Natta catalyst system.

2. Description of the Related Art

Various types of polyethylene are known in the art. Low densitypolyethylene (LDPE) is generally prepared at high pressure using freeradical initiators and typically has a density in the range of0.9100-0.9400 g/cc. High density polyethylene (HDPE) usually has adensity in the range of 0.9400 to 0.9600 g/cc, which is prepared withZiegler-Natta type catalysts or single-site type catalysts (such asmetallocene catalysts) at low or moderate pressures. HDPE is generallypolymerized without comonomer, or alternatively with a small amount ofcomonomers with fewer short chain branches (SCB) than LLDPE. Linear lowdensity polyethylene (LLDPE) is one of the ethylene/alpha-olefinscopolymers, generally prepared in the same manner as HDPE, except itincorporates a relatively higher amount of alpha-olefin comonomers suchas 1-butene, 1-hexene or 1-octene.

LLDPE copolymers have short branches along the main chain due to theunits derived from the alpha-olefin comonomers. These comonomer orbranches distribution along the polymer chain are crucial because itinfluences the properties of the copolymer resin which, in turn,determine its applicability for commercial LLDPE products. For example,a good comonomer distribution ensures the achievement of an ethylenecopolymer having a density sufficiently lower than HDPE, whilecontrolling the amount of fractions soluble in hydrocarbon solvent (likehexane or xylene) that worsen certain properties of the said copolymers,such as increasing the blocking phenomenon observed in rolls of LLDPEfilm. By narrowing molecular weight distribution, lowering the densityof LLDPE, improving branching or comonomer distribution, reducing lowmolecular weight extractable fractions (the short chain branchingcontent in high molecular weight fractions are desirable), tearstrength, impact strength, puncture resistance, toughness, and clarityproperties of films from LLDPE resins are significantly improved.

Transition metal catalyst systems, including Ziegler-Natta catalysts,metallocene catalysts, and other single-site catalysts, are widely usedfor producing LLDPE in slurry, gas phase, or solution processes. Thecatalyst composition used for producing linear low density polyethylene(LLDPE) determines the properties of the polymers. Thus, the catalystcomposition allows for tailoring molecular structure and properties ofthe polymer resins.

Conventional Ziegler-Natta catalyzed polyethylene copolymers, such asLLDPE, have both a relatively broad molecular weight distribution and arelatively broad comonomer distribution. As such, comonomers arepredominately incorporated into the low molecular weight polymermolecules or short polyethylene chains, whereas the long polyethylenechains or high molecular weight polymer molecules do not contain ameaningful amount of comonomers. In other words, the conventionalZiegler-Natta catalyzed ethylene copolymers exhibit a heterogeneous SCBdistribution among polymer chains of different molecular weight. Thislack of compositional homogeneity is associated with severaldisadvantages including “organoleptic” problems caused by low molecularweight material and suboptimal impact strengths, which are believed tobe caused by the crystallinity of the homopolymer fraction. Therefore,conventional Ziegler-Natta catalyzed LLDPE exhibiting a broadcomposition distribution and broad molecular weight distribution isknown to have good processability as measured by extruder pressures andmotor load. In film applications, conventional Ziegler-Natta catalyzedLLDPE (ZN LLDPE) exhibits good physical properties as related to tensileand tears (MD tear and TD tear) strengths, but shows low dart dropimpact strength and puncture strength and clarities.

Metallocene or single-site catalysts normally produce resins with anarrow composition distribution in which comonomers are substantiallyuniformly distributed among the polymer chains of different molecularweight. Metallocene or single-site catalyzed LLDPE (mLLDPE), having anarrow composition distribution and narrow molecular weightdistribution, is known to produce tough films with high dart impact andpuncture resistance and excellent optical properties. But themetallocene or single-site catalyzed LLDPE exhibits adverseprocessability and weak film tensile properties (e.g. MD tear strength).In addition, it is difficult to apply metallocene or single sitecatalysts in existing polymerization processes without major processmodification and capital investment. This is because the solubility oforganometallic compounds and cocatalysts, such as methylaluminoxane(MAO), requires costly immobilization processes on inorganic supports toobtain good operability while maintaining acceptable catalyst activityin a supported metallocene system.

As such, advanced Ziegler-Natta catalyst and its compositions havealready widely attracted the industry's attention. It is desirable thatadvanced Ziegler-Natta catalyst can produce ethylene copolymer and LLDPEhaving properties of both conventional ZN-made LLDPE andmetallocene-made mLLDPE. Specifically, it is highly desirable to attainpolyethylene resins that exhibit ZN LLDPE type processability and a tearstrength that is higher than or equivalent to ZN LLDPE, but with a dartimpact strength and optical property comparable to or better than thatof mLLDPE.

U.S. Pat. Nos. 5,258,345 and 5,550,094 disclose a Ziegler-Natta catalystsystem, which comprises a silica supported catalyst precursor and anactivator of dimethlyaluminum chloride (DMAC), for producing LLDPEpolymers with a bimodal MWD, particularly those containing a highmolecular weight fraction. The catalyst precursor is prepared bycontacting a carrier (such as silica) with an organomagnesium compound(such as dibutylmagnesium) to incorporate magnesium into the carrier,and then treating the carrier in sequence with a silicon compound, atransition metal compound, and an organomagnesium compound. Theprecursor can be activated with DMAC or a mixture of DMAC and atrialkylaluminum compound. However, DMAC alone as activator showsrelatively low activity and alpha olefin oligomerization, which may foula gas phase fluidized bed polymerization reactor. High ratio of DMAC totrialkylaluminum (30:1 to 300:1) is required to achieve broad molecularweight distribution and maintain high molecular weight tail. U.S. Pat.Nos. 5,210,167 and 5,258,449 report the film properties of the LLDPEpolymers made from this catalyst precursor activated with DMAC or withdiethylaluminum chloride (DEAC)/tri(n-hexyl)aluminum (TnHAL)pretreatment and DMAC activation. The LLDPE polymer films contain asignificant portion of high molecular weight components with anM_(z)/M_(w) ratio of greater than 3.5, and exhibit improved opticalproperties and impact properties. However, the dart impact strength isstill much lower than that from typical m-LLDPE polymers. The otherpolymer properties, such as comonomer compositional distribution, MDtear strength, and processability, such as melt pressure and meltstrength, are not mentioned.

U.S. Pat. Nos. 6,043,326 and 8,546,499 disclose a process forcopolymerizing ethylene and alpha-olefins using a halogen compound basedprocatalyst and a cocatalyst from a 1:1 mixture of TEAL/EADC orTEA/DEAC. The procatalyst is prepared by depositing an alkyl metalchloride (a product from a branched aliphatic monoalcohol and Mgdialkyl), a chlorine-containing Ti compound (TiCl₄), onto an inorganicsupport, such as EADC treated silica. Relatively high Al/Ti ratio (>15)is needed for achieving decent polymerization activity and productivityand large amount of chain transfer agent (H₂) required for regulatingmolecular weight of the product. The resulting LLDPE polymers show moreuniform comonomer composition distribution profile across the molecularweight distribution, compared to LLDPE produced without using ahalogenated cocatalyst. However, there is no mention of theprocessability and melt strength, physical properties (dart impact andtear strengths), and optical properties (haze, clarity and gloss) of theproduct.

Accordingly, a new catalyst and/or process is needed having good processoperability and high polymerization activity, and for producing LLDPEpolymers which have the merits of both ZN LLDPE and m-LLDPE, such asdesirable molecular weight and molecular weight distribution, as well asuniform comonomer composition distribution, which provide blown filmswith desirable physical properties such as high MD tear and dart impartstrengths, excellent optical properties, and good processability. Ideapolymer composition has unique features and then thereby produce theblown films having processability that better than or equal to ZNcatalyzed LLDPE, and a MD tear strength that is higher than super-hexeneZN LLDPE and dart impact strength that is on a par with m-LLDPE.

Assignee's prior patents, such as U.S. Pat. Nos. 7,618,913, 8,993,693,and 9,487,608, describe a highly active supported Ziegler-Natta catalystsystem with a nitrogen-based electron donor for producing uniqueethylene copolymer. Both catalyst component and a prepolymerizedcatalyst component, activating with trialkylaluminum compound, produceethylene-based polymer or co-polymer (LLDPE) having a narrower molecularweight distribution, a more uniform comonomer composition distribution,and better mechanical properties, such as dart impact and tearstrengths. The blown films from the said LLDPE polymer show a MD tearstrength that is higher than super-hexene ZN LLDPE and dart impactstrength in par with m-LLDPE. Fractionation analysis of the LLDPEpolymer showed that high molecular weight fractions with M_(w)>300,000g/mol have flat comonomer composition distribution. However, theintrinsic viscosity of these fractions conforms to the Mark-Houwinkequation, indicating only linear structure exists in these high MWfractions. The linear and very high molecular weight polymer chains tendto form thicker crystallization lamella and causes rough surface forblown films. Accordingly, the optical properties with haze of films madewith the LLDPE polymer need to be further improved to compete with thosefrom an advanced m-LLDPE or ethylene/1-octene copolymer (C8-LLDPE), madeby solution process. The optical properties limit their specificapplications for high clarity films. In addition, the non-linearstructure with a given amount of long chain branching is desirable forimproving rheological behavior and processability of polymer. Forexample, the melt strength of the said polymer is not sufficient forspecific applications requiring certain extensional flow propertiesduring processing, such as blow molding and geomembrane application.

Thus, there is still further demand for development of linear lowdensity polyethylene (LLDPE) showing more constant commoner compositiondistribution profiles across the MWD (the comonomer content of thecopolymer does substantially not decrease with increasing molecularweight, compared to state of prior art LLDPEs) and/or even showing anupward comonomer composition profile across the MWD (the comonomercontent of the copolymer increases as the molecular weight of thepolymer chains increases). In addition, such polyethylene copolymershave sporadic long chain branches and high molecular weight tail alongwith a reversed comonomer distribution. Such LLDPEs should have asubstantially constant distribution of molecular weight profile acrossthe chemical composition distribution or polymer fractions, meaning thatmolecular weight is more constant, respectively flat, from solubleand/or insoluble fractions over elution temperature range from 30° C. to130° C.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a linearlow density polyethylene with improved properties, such as molecularweight, comonomer composition distribution, amount of CRYSTAF solublepolymer fraction and density, amount of long chain branching and itsdistribution, and high molecular weight tail and chain entanglement witha reversed comonomer distribution. In particular, the object of theinvention is to provide an improved comonomer composition distribution,improved molecular weights of individual polymer fractions, comonomercontents in different polymer chains, and side chain distribution insingle polymer chains. More specifically, the object of the presentinvention is to tune the microstructure of the polymer component fortailoring polymer properties, where the polymer microstructure includescrystallizing polymer component (fraction) distribution byCrystallization Analysis Fractionation (CRYSTAF) and Temperature RisingElution Fractionation (TREF), molecular weight and molecular weightdistribution, comonomer composition distribution, and the long chainbranching content in low molecular weight and high molecular weightfractions, and molecular weight and comonomer distribution in highmolecular weight tail. Ethylene/alpha-olefin copolymer or linear lowdensity polyethylene (LLDPE) with such desirable microstructure providesthe corresponding blown films with improved processability, enhancedmelt strength, and improved optical properties comparable to mLLDPE andC8 LLDPE, while maintaining higher MD tear strength than super-hexene ZNLLDPE and superior dart impact strength on par with m-LLDPE.

What is disclosed is a Ziegler-Natta catalyst composition comprising aspecial procatalyst containing titanium, magnesium, chlorine, electrondonors and silane compounds, supported on a particulate inorganiccarrier, and a halogenated aluminum alkyl or organohalogenous aluminumcompound as cocatalyst for the production of the ethylene/alpha-olefinscopolymers, according to the teachings of the present invention.

In one embodiment of the present invention, a Ziegler-Natta catalyzedethylene/alpha-olefins copolymer or linear low density polyethylene isprovided having the following properties:

-   -   density, according to ASTM D1505-98, of between 0.890 and 0.935        g/cc;    -   C4-C10 comonomer content, determined by Fourier transform        infrared spectroscopy, of between 1 and 20 wt %;    -   melt index (12), according to ASTM D1238, of between 0.5 and 10        dg/min;    -   ratio (M_(z)/M_(w)) of z-average molecular weight (Mz) to weight        average molecular weight (Mw) of between 3.0 and 10;    -   melting point of the copolymer is over 124° C. across the        density of from 0.890 to 0.935 g/cc;    -   sporadic long chain branches with J-C α value (LCB per 10⁶ total        carbon atoms) of less than 5.    -   melt strength index, defined as the ratio of storage modulus to        loss modulus (G′/G″) at a shear rate of 0.03 s⁻¹, is from 0.1 to        5.    -   weight average molecular weight Mw, determined by gel permeation        chromatography, of less than 200,000 g/mol,    -   a fraction soluble at a temperature below 30° C. of at least 12        wt %, determined by CRYSTAF, having a weight average molecular        weight Mw, determined by gel permeation chromatography, of        higher than 90,000 g/mol, and a fraction between 60 and 75° C.        of less than 35 wt % and    -   Greater than 13.5 wt % of a polymer component having an elution        temperature below 30° C., determined by temperature rising        elution fractionation (TREF) analysis;    -   Greater than 15 wt % of a polymer component having an elution        temperature below 40° C. (average high molecular weight of about        or higher than 90,000 g/mol);    -   Greater than 10 wt % of a polymer component having an elution        temperature range from 30° C. to 60° C.;    -   Less than 50 wt % of a polymer component having an elution        temperature range from 60° C. to 94° C.;    -   Greater than 25 wt % of a polymer component having an elution        temperature higher than 94° C.;    -   Greater than 5 wt % of a polymer component (average high        molecular weight of higher than 150,000 g/mol) having an elution        temperature range from 100° C. to 130° C.;    -   a substantially constant distribution of short chain branching        profile across its molecular weight distribution (MWD) in each        fraction over the elution temperature range from 30° C. to 100°        C., determined by Gel Permeation chromatography coupled with        Fourier transform infrared spectroscopy detector (GPC-FTIR); and    -   a high molecular weight tail in the fractions over the elution        temperature range from 100° C. to 130° C. and a reversed        distribution of comonomer composition profile across the        molecular weight distribution, determined by Gel Permeation        chromatography coupled with Fourier transform infrared        spectroscopy detector (GPC-FTIR).

The ethylene/alpha-olefin copolymer or linear low density polyethyleneaccording to certain teachings of the present invention is prepared bycopolymerizing ethylene with one or more C4-C10 comonomer in thepresence of a special Ziegler-Natta catalyst system comprising:

-   -   A) a precursor prepared by contacting [A1] a magnesium-based        composite support, in-situ prepared by contacting metallic        magnesium with alkyl halide or aromatic halide in the presence        of an organic silicon compound having the formula R¹        _(m)Si(OR²)_(n), wherein R¹ and R² are C₁-C₂₀ hydrocarbyl,        m=0-3, n=1-4, and m+n=4, and wherein each R¹ and each R² may be        the same or different, with [A2] a compound having the formula        R³ _(x)SiX_(y), wherein R³ is C₁-C₂₀ hydrocarbyl, X is halogen,        x=0-3, y=1-4, and x+y=4, and wherein each X and each R³ may be        the same or different, [A3] a compound having the formula MX₄,        wherein M is an early transition metal such as Ti, [A4] a        compound having the formula M(OR⁴)_(a)X_(4-a), wherein M is an        early transition metal such as Ti, wherein R⁴ is C₁-C₂₀        hydrocarbyl, X is halogen, and 0≤a≤4, [A5] a substituted        aromatic compound containing nitrogen such as        2,6-dimethylpyridine and 8-quinolinol and 2-methyl-8-quinolinol,        and [A6] an alkyl halide or aromatic halide compound having the        formula R⁵X, wherein R⁵ is C₁-C₂₀ hydrocarbyl.    -   B) a cocatalyst, which is preferably a halogenated aluminium        alkyl or organohalogenous aluminum compound prepared in-situ by        reacting alkyl aluminum and/or alkylaluminoxane with halogenated        alkylaluminum compound.

In another embodiment of the present invention, theethylene/alpha-olefin copolymer or linear low density polyethylene isprepared by copolymerizing ethylene with one or more C4-C10-comonomer inthe presence of a prepolymerized catalyst. The prepolymerized catalystcomposition is one type of prepolymer prepared by (co)polymerizingethylene and/or alpha olefins in the presence of (A) a Ziegler-Nattacatalyst and (B) cocatalyst, which is preferably a halogenated aluminiumalkyl and/or an organohalogenous aluminum compound obtained in-situ byreacting alkylaluminoxane with halogenated alkylaluminum compounds. Thesaid prepolymer has an amount ranging from 0.1 to 1000 g per g of thesolid catalyst precursor, being characterized by its sporadic long chainbranches in the high molecular weight fractions and an improvedcomonomer response for the copolymerization of ethylene and alpha-olefinwithout using additional co-catalyst.

In yet another embodiment, a polyethylene film is made with theethylene/alpha-olefin copolymer or linear low density polyethylene inaccordance with certain teachings of the present invention, having abalance of improved physical, optical, mechanical properties as well asimproved processability. The film includes a 1% secant modulus ofgreater than 25,000 psi, a film haze of less than 10, a film clarity ofgreater than 90, a dart impart resistance of greater than 500 g/mil, anda MD tear strength of greater than 500 g/mil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts rheological curves for Inventive Example 1 andComparative Example 1.

FIG. 2 depicts rheological curves for Inventive Example 1 andComparative Example 2.

FIG. 3 depicts GPC curves of Inventive Example 1 and ComparativeExamples 1 and 2.

FIG. 4 depicts GPC curves of Inventive Example 1 and ComparativeExamples 4 and 5.

FIG. 5 depicts curves of intrinsic viscosity and dW_(f)/d(log M) as afunction of molecular weight for Inventive Example 1 and ComparativeExample 1.

FIG. 6 depicts curves of intrinsic viscosity and dW_(f)/d(log M) as afunction of molecular weight for the Inventive Example 1 and theComparative Example 2.

FIG. 7a is the GPC-FTIR curve for SCBD profile across its molecularweight distribution (MWD) in the fraction eluted at temperature of lessthan 35° C.;

FIG. 7b is the GPC-FTIR curve for SCBD profile across its molecularweight distribution (MWD) in the fraction eluted at temperature of35-94° C.;

FIG. 7c is the GPC-FTIR curve for SCBD profile across its molecularweight distribution (MWD) in the fraction eluted at temperature of94-100° C.;

FIG. 7d is the GPC-FTIR curve for SCBD profile across its molecularweight distribution (MWD) in the fraction eluted at temperature of over100° C.

DETAILED DESCRIPTION OF THE INVENTION

The catalyst composition and polymerization process of the presentinvention provides for the production of ethylene/alpha-olefin copolymeror linear low density polyethylene (LLDPE) with the above described“tailored” and “fine-tuned” polymer microstructure and properties. Inparticular, the catalyst composition of the present invention allows forproducing such ethylene copolymers with improved properties such ascomonomer composition distribution, short chain branching distribution,high molecular weight tail, long chain branching content in polymerchain (fraction), and molecular weight and molecular weight distributionin each fraction over elution temperature.

The inventors have found that comonomer composition distribution (CCD)and short chain branching distribution (SCD) have positive effects onpolymer properties, such as optical properties, crystallinity,toughness, and many other properties. The polymers according to thepresent invention show balanced/improved comonomer compositiondistribution and short chain branching distribution. In particular, asubstantially constant distribution of short chain branching profileacross its molecular weight distribution (MWD) in each fraction over theelution temperature range from 30° C. to 100° C. can be reached.Moreover, a high molecular weight tail in the fractions over elutiontemperature range from 100° C. to 130° C. and a reversed distribution ofcomonomer composition profile across the molecular weight distributioncan be obtained by using the catalyst composition of the presentinvention.

It has been discovered that molecular weight, molecular weightdistribution, and short chain branching distribution of soluble fractioneluted below a temperature of 40° C. are critical to polymer propertiessuch as toughness (dart impact), MD tear strength, and blockingproperties or cling properties. The polymer according to the presentinvention contains at least 13.5 wt % of a soluble fraction eluted belowa temperature of 30° C., and at least 15 wt % of a soluble fractioneluted below a temperature of 40° C. These fractions have both a narrowmolecular weight distribution, a high molecular weight greater thanabout 100,000 g/mol, and a constant or reversed distribution ofcomonomer composition profile across the molecular weight distribution,which are similar to other fractions eluted from 40° C. to 100° C. It isbelieved that this unique polymer features in the soluble fractioneluted below 40° C. is associated to toughness (dart impact resistance),MD tear strength, tensile strength, and cling properties.

To improve the melt strength and processability and optical properties,it is desirable that the polymer of the present invention should have ahigher ratio of average viscosity molecular weight (Mz) to averageweight molecular weight (Mw), while maintaining the above-mentionedpolymer features and polymer composition. In particular, high molecularweight tail or bump is more desirable. The polymer according to thepresent invention contains a high molecular weight tail, together withM_(z)/M_(w) ratio of greater than 3.5. In U.S. Pat. Nos. 5,258,345 and5,550,094 and 5,210,167 and 5,258,449 disclosed a Ziegler-Natta catalystsystem comprising a silica-supported catalyst precursor and an activatorof dimethylaluminum chloride (DMAC) for producing LLDPE polymers with abimodal MWD and a high molecular weight tail. However, catalyst systemsin these prior arts demonstrate very low activity, the polymer producedthereof contain alpha olefin oligomer (low molecular weight fraction)that may foul a gas phase fluidized bed polymerization reactor. U.S.Pat. Nos. 5,210,167 and 5,258,449 disclosed the film properties of theLLDPE polymers with improved optical properties and dart impactresistance. Due to soluble fraction containing low molecular weight andnon-even short chain branching distribution in the polymer, therefore,the dart impact strength and MD tear strength are still much lower thansuper-hexene or typical m-LLDPE polymers. This is indication thatpolymer composition in these prior arts is significant from polymercomposition in this invention as mentioned above.

Moreover, long chain branching in polyethylene polymer also has aninfluence on polymer properties, such as crystallization kinetics,crystal structure, relaxation time, melt elasticity, optical properties(haze, clarity, and gross), processability, melt strength, polymerviscosity and rheology behavior, and output rate in film production aswell. Chromium-based catalysts and metallocene-based catalysts canproduce polymers with long chain branching content therein, whiletitanium-based Ziegler-Natta catalyst rarely create long chain branchingin the polymer chain. Chromium-based catalyst produces polymer havingvery broad molecular weight distribution and very high amount of longchain branching in polymer, which leads to poor toughness and weak MDtear strength and high haze, although there is excellent processabilityand melt strength. Some metallocene-based catalyst systems (i.e., U.S.Patent Application No. 2006/0100401A1) demonstrate that the metallocenecomposition and polymerization methods therein provide ethylene polymerswith long chain branch in the polymer chain, which can improve haze andclarity in the blown film while minimizing impact on other propertiessuch as dart impact. However, MD tear strength of polymer is much lowerthan Ziegler-Natta catalyzed ethylene copolymer due to too much longchain branch content therein in the polymer. U.S. Pat. No. 8,475,899disclosed a metallocene-based process for producing broad molecularweight distribution polymers with a reverse comonomer distribution andlow levels of long chain branches less than 8 per 10⁶ total carbonatoms, and less than about 5% by weight of the polymer eluted below atemperature of 40° C. There is no data to show that polymer with lowlevels of long chain branches therein have better film opticalproperties and toughness, together with mechanical propertiesimprovement such as MD tear strength. On the other hand, the compositiondisclosed in U.S. Pat. No. 8,475,899 is much different from thatprovided in this invention, based on TREF analysis.

The optical improvement (haze decrease and clarity increase) is observedwith increasing melt elasticity in LLDPE films, either by addition ofbranched molecules or high molecular weight molecules. However, theintroduction of LCB does not appear to provide an improvement for bothprocessing and film performance, long chain branch in polymer canimprove film optical properties, processability and bubble stability,but will decrease Elmendorf MD tear strength, as suggested in theliteratures: for examples, Paula Cristina Dartora, Ruth MarleneCampomanes Santana, and Ana Cristina Fontes Moreira, “The influence oflong chain branches of LLDPE on processability and physical properties”,Polimeros 26 (6), 2015; Ashish M. Sukhadia, David C. Rohlfing, Garth L.Wikes, and Matthew B. Johnson, “Optical haze properties of polyethyleneblown films: Part 2—the origins of various surface roughnessmechanisms”, SPE ANTEC 2001 May 6-10; each of which is incorporatedherein by reference. Therefore, it is believed that there is an optimumlevel of LCB in polymer chain that improves both processing andproperties (i.e., optical properties and MD tear resistance). It wasfound in this invention that level of long chain branches less than 1per 10⁶ total carbon atoms has positive influence to improve bothmechanical properties such as MD tear strength and optical properties aswell.

In order to tailor LLDPE polymer composition with the desirablemicrostructures, including short chain branching distribution, molecularweight distribution, high molecular weight in the fraction eluted overtemperature from 20° C. to 40° C., high molecular weight tail, and lowlevel of long chain branches less than 1 per 10⁶ total carbon atoms inthe polymer composition, we further improve the catalyst system anddevelop a compatible polymerization process through which catalyst andpolymerization process morphology and flowability is improved, operationefficiency of producing LLDPE polymers with lower density could beenhanced without issues of reactor fouling, catalyst activity andcatalyst productivity could be enhanced, and the above-mentionedmicrostructure of the LLDPE polymers could be tuned. Theethylene/alpha-olefins copolymer or linear low density polyethylene ofthe present invention is made with an advanced magnesium-based catalystprecursor, and/or a special ethylene prepolymerized catalyst component,a process for preparing the ethylene prepolymer from the catalystprecursor, and a process for making such polyethylene copolymers.

The present invention includes a process to produce ethylene(co)polymers that includes reacting at least the following componentswith each other:

-   -   (a) an advanced Ziegler-Natta catalyst precursor comprising Ti,        Mg, Si, halogen and nitrogen.    -   (b) a cocatalyst comprising a halogenated aluminum alkyl or        organohalogenous aluminum compounds prepared in-situ by reacting        alkyl aluminum and/or alkylaluminoxane with halogenated        alkylaluminum compound;    -   (c) ethylene, and    -   (d) one or more alpha-olefins copolymerizing with ethylene,        being characterized in that the organohalogenous aluminum        compound is in-situ prepared by reacting alkyl aluminium and/or        alkylaluminoxane with halogenated alkylaluminum during        (co)polymerization.

The present invention also includes another process to produce theethylene copolymer, comprising reacting of at least the followingcomponents with each other:

-   -   (a) a prepolymer (prepolymerized catalyst component) prepared        from the polymerization of ethylene with or without one or more        alpha-olefins, optionally under hydrogen, in the presence of (i)        an advanced Ziegler-Natta catalyst precursor comprising Ti, Mg,        Si, halogen and nitrogen, and (ii) an activator comprising a        halogenated aluminum alkyl or organohalogenous aluminum        compounds produced by reacting alkyl aluminum and/or        alkylaluminoxane with halogenated alkylaluminum compound;    -   (b) ethylene, and    -   (c) one or more alpha-olefins copolymerizing with ethylene        without a co-catalyst in the presence of hydrogen.

In yet another embodiment, the resins of the present invention exhibit aunique composition which provide the corresponding blown films withimproved processability, bubble stability, enhanced melt strength, andimproved optical properties equal or comparable to mLLDPE and C8 LLDPE,while maintaining outstanding MD tear strength higher than ZN catalyzedLLDPE or super-hexene ZN LLDPE and superior dart impact strength on parwith m-LLDPE.

Catalyst Component and its Preparation

The catalyst precursor discussed above is prepared by the followingreaction, as depicted schematically and described in detail as follows:

Mg+R¹ _(x)SiX_(y)+R² _(m)Si(OR³)_(n)+MX₄+M(OR⁴)₄+N-base ligand+R⁵X→→

M(OR⁴)Cl₃·N-base ligand·Mg(OR⁴)Cl·MgCl₂ (catalyst precursor)+R²_(m)Si(OR³)_(n)X_(4-m-n)+R⁵MgX+byproducts (alkanes)

Firstly, an organic silicon complex is prepared in situ by reactingalkoxysilane ester, R² _(m)Si(OR³)_(n), with halogen-substituted silane,R¹ _(x)SiX_(y). The reaction is preferably conducted in the presence ofmagnesium and halogenated alkyl group, such as alkyl chloride, which,without being limited to this position, is believed to form alkylmagnesium halide. The mixture is heated for 30 to 60 minutes, preferably45 to 60 minutes, in a non-polar solvent to about 50 to 100° C.,preferably to about 65 to 85° C.

The reactions between alkoxysilane ester with halogen-substituted silanesuch as silicon tetrachloride (SiCl₄) are described by M. G. Voronkov,V. P. Mileshevich, and A. Yu in the book “The Siloxane Bond”, PlenumPublishing Corp., New York, 1978. The reaction can be carried out in anon-polar solvent by heating the mixture to about 50 to 100° C.,preferably to about 65° C. to 85c° C. The duration of heating is notgenerally critical. One acceptable procedure is to heat for about 30 to60 minutes once the desired temperature is obtained. The molar ratio ofalkoxysilane ester to halogen-substituted silane is from about 0.5 to3.0, and more preferably from about 0.8 to 1.5. Some percentage of thealkoxysilane ester may remain in excess and thus, not reacted, in thefinal organic silicon product. The organic silicon product can be andpreferably is used in the next steps in situ without further separationor characterization.

The halogen-substituted silane has the formula R¹ _(x)SiX_(y) where R¹is a C₁-C₂₀ hydrocarbyl, which for present purposes includes bothunsubstituted and substituted species, including halogen substitutedspecies, X is halogen, x is 0-3, y is 1-4, and x+y=4. More than onehalogen X may be employed in the halogen-substituted silane. Suitablehalogen-substituted silane compounds include, but is not limited to,silicon tetrachloride, tetrabromosilane, tetrafluorosilane,benzyltrichlorosilane, bis(dichlorosilyl)methane,2-bromoethyltrichlorosilane, t-butyldichlorosilane,t-butyltrichlorosilane, 2-(carbomethoxy)ethyltrichlorosilane,2-chloroethylmethyl dichlorosilane, 2-chloroethyltrichlorosilane,1-chloroethyltrichlorosilane, chloromethylmethyldichlorosilane,((Chloromethyl)phenylethyl)trichlorosilane, chloromethyltrichlorosilane,2-cyanoethylmethyldichlorosilane, cyclohexyltrichlorosilane,cyclopentyltrichlorosilane, cyclotetraemethylenedichlorosilane,cyclotrimethylenedichlorosilane, 1,5-dichlorohexamethyltrisiloxane,(dichloromethyl)trichlorosilane, dichlorosilane,1,3-dichlorotetramethyldisiloxane, diethyoxydichlorosilane,ethylmethyldichlorosilane, ethyltrichlorosilane, heptyltrichlorosilane,hexachlorodisilane, hexachlorodisiloxane, isobutyltrichlorosilane,methyltrichlorosilane, octyltrichlorosilane, pentyltrichlorosilane,propyltrichlorosilane, and trichloromethyltrichlorosilane. It ispreferred to employ tetrachlorosilane, allyltrichlorosilane,ethyltrichlorosilane, methyltrichlorosilane, or dichlorodiphenylsilane.

Suitable alkoxysilane ester compounds have the formula R²_(m)Si(OR³)_(n). R² and R³ are independently selected from any C₁-C₂₀hydrocarbyl, which for present purposes includes both unsubstituted andsubstituted species, including halogen substituted species, m is 0-3, nis 1-4, and m+n=4. More than one hydrocarbyl or substituted hydrocarbylgroup may be employed as the R² component, and more than one hydrocarbylor substituted hydrocarbyl group may be employed as the R³ component.Suitable alkoxysilane ester compounds include, but is not limited to,tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane,tetrapropoxysilane, tetraethoxysilane, tetraisobutoxysilane,tetraphenoxysilane, tetra(p-methylphenoxy)silane, tetrbenzyloxysilane,tetrakis(2-methoxyethoxy)silane, tetrakis(2-ethylhexoxy)silane,tetraallyloxysilane, methyltrimethoxysilane, methyltriethoxysilane,mehtyltributoxysilane, methyltriphenoxysilane, ethyltriethoxysilane,ethyltriisobutoxysilane, ethyltriphenoxysilane, allyltrimethoxysilane,octadecyltrimethoxysilane, octadecyltriethoxysilane,octyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane,benzyltriphenoxysilane, methyltrialllyloxysilane,dimethyldimethoxysilane, dimethyldiethoxysilane,dimethyldiisopropyloxysilane, dimethyldibutoxysilane,dimethyldihexyloxysilane, dimethyldiphenoxysilane,diethyldiethoxysilane, diethyldiisobutoxysilane, diethyldiphenoxysilane,dibutyldiisopropyloxysilane, dibutyldibutoxysilane,dibutyldiphenoxysilane, diisobutyldiethoxysilane,diisobutyldiisobutoxysilane, diphenyldimethoxysilane,diphenyldiethoxysilane, diphenyldibutoxysilane, dibenzyldiethoxysilane,divinyldiphenoxysilane, diallyldipropoxysilane, diphenyldiallyoxysilane,1,1,1,3,3-pentamethyl-3-acetoxydisiloxane, triethoxysilane,trimethoxysilane, triethoxychlorosilane, and trimethoxychlorosilane.Particularly preferable compounds are tetramethoxysilane,tetraethoxysilane, tetraisopropoxysilane, tetrapropoxysilane,tetrabutoxysilane, tetraisobutoxysilane, or combinations thereof.

Secondly, the organic silicon complex or organic silicon complexcontaining nitrogen is contacted with a transition metal compound,preferably a titanium compound, to form an organic silicon complexcontaining transition metal. The molar ratio of silicon complex to thetitanium compound is preferably from about 0.1 to 3.0, and morepreferably from about 0.5 to 2.0. The reaction is preferably conductedat 80° C., and the duration of heating may be from about 30 to 60minutes, preferably about 40 minutes. Once the desired temperature isobtained, the reaction generates an organic silicon complex containingtransition metal, which is typically a brown product when titanium isemployed. The organic silicon complex containing transition metal can beused, and desirably is used, for the following steps in situ withoutfurther separation or characterization.

The transition metal compounds that are acceptable for this processinclude alkoxytitanium halide compounds having the formulaTi(OR⁴)₄X_(4-n). R⁴ is a C₁-C₂₀ hydrocarbon, X is a halogen, and 0≤n≤4.For present purposes, R⁴ may be unsubstituted or substituted, includinghalogen substituted. Each R⁴ may be the same or different. The titaniumcompound Ti(OR⁴)₄X_(4-n) may be prepared in situ prepared by reacting atitanium halide compound with Ti(OR⁴)₄ and/or Ti(OR⁴)₃X or by reactingcorresponding alcohol, R⁴OH, with a titanium halide compound.Alternatively, Ti(OR⁴)₄X_(4-n) may be formed before addition to thereactor by preconditioning a titanium halide compound with Ti(OR⁴)₄,Ti(OR⁴)₃ or R⁴OH. Preconditioning may be achieved by mixing a titaniumhalide compound in hexane with Ti(OR⁴)₄ or Ti(OR⁴)₃ in hexane andstirring at about 75° C. to 80° C. for about 0.5 to 1 hour, resulting ina Ti(OR⁴)₄X_(4-n) complex.

Examples of the titanium halide compound include TICl₄, TiBr₄, TiI₄,TiCl₃.nTHF and 3TiCl₃.AlCl₃. Among these titanium halides, TiCl₄ and3TiCl₃AlCl₃ are preferred. Titanium compounds with the structuralformula Ti(OR⁴)₄ or Ti(OR⁴)₃X include, but are not limited to,trimethoxymonochlorotitanium, triethoxyfluorotitanium,triethoxychlorotitanium, tetraethoxytitanium, tripropoxyfluorotitanium,tripropoxychlorotitanium, tetra-n-propoxytitanium,tetraisopropoxytitanium, tributoxyfluorotitanium,tributoxychlorotitanium, triisobutoxychlorotitanium,tetra-n-butoxytitanium, tetra-isobutoxytitanium,dipentoxydichlorotitanium, tripentoxymonochlorotitanium,tetra-n-pentyloxytitanium, tetracyclopentyloxytitanium,trioctyloxymonochlorotitanium, 2-ethylhexoxytitanium trichloride,butoxytitanium trichloride, tetra-n-hexyloxytitanium,tetracyclohexyloxytitanium, tetra-n-heptyloxytitanium,tetra-n-octyloxytitanium, tetra-2-ethylhexyloxytitanium,tri-2-ethylhexyloxymonochlorotitanium, tetranonyloxytitanium,tetradecyloxytitanium, tetraisobornyloxytitanium, tetraoleyloxytitanium,tetraallyloxytitanium, tetrabenzyloxytitanium,tetrabenzohydryloxytitanium, triphenoxytitanium,tetr-o-methylphenoxytitanium, tetraphenoxytitanium,tetra-o-methylpheoxytitanium, tetra-m-mehtylpheoxytitanium,tetra-o-methylphenoxytitanium, tetra-m-methylphenoxytitanium,tetra-1-naphthyloxytitanium, tetra-2-napthyloxytitanium and mixturesthereof. The preferred Ti(OR⁴)₄ or Ti(OR⁴)₃X compounds are2-ethylhexoxytitanium trichloride, butoxytitanium trichloride,tetra-n-propoxytitanium, tetraisopropoxytitanium,tetra-n-butoxytitanium, tetraisobutoxytitanium,dibutoxydichlorotitanium, isobutoxytrichlorotitanium andpropoxytrichlorotitanium.

Thirdly, the organic silicon complex containing titanium is furthercontacted with a substituted aromatic ring nitrogen compound to form acomplex containing Si—Ti—N compounds. The substituted aromatic ringnitrogen compound is preferably employed in amounts sufficient to have amolar ratio of substituted aromatic ring nitrogen compound to transitionmetal compound as added in the previous processing step of typicallyfrom about 0.010:1 to 50:1, preferably from about 0.02:1 to 10:1, andmost preferably from about 0.1:1 to 5:1. Although the conditions are notgenerally critical, one acceptable procedure is to heat at about 80° C.for about 30 to 100 minutes, preferably about 60 minutes. Once thedesired temperature is obtained, the reaction generates a complex withdark brown color. The said complex can be used, and preferably is used,for the next steps in situ without further separation orcharacterization.

The N-base ligand compounds as an electron donor is a substitutedaromatic ring nitrogen compound, and can be selected from thesubstituted pyrimidine, dipyridyl, pyrazine, terpyridine and quinolinecompounds. Representative examples of the compounds include, but are notlimited to, 2,6-dimethylpyridine, 2,6-diisopropylpyridine,2,6-di-tert-butylpyridine, 2,4,6-trimethylsilylpyridine,2,6-dimethoxypyridine,2,6-bis(chloromethyl)-pyridine,2,2′:6′,2′-terpyridine, 2,2′-dipyridyl,6,6′-dimethyl-2,2′-dipyridyl, 2,2′-diquinolyl,4-(p-tolyl)-2,2′:6′,2″-terpyridine, 2,6-dimethypyrazine,2,3,5-trimethylpyrazine, 2,4,6-trimethyl-s-triazine,2,3,5,6-tetramethylpyrazine, quinaldine, pyrimidine, pyrazine,pentafluoropyridine, pentachloropyridine, 2,4,6-trimethylpyrimidine,3-methylpyridazine, 2,6-dimethylpyridazine, 2,6-pyridinecarboxylic acid,2,6-pyridinediacetate, 2,6-pyridinecarbonyl dichloride,2,6-pyridinecarboxaldehyde, 2,6-pyridinedicarboxamide,2,6-pyridinedimetanol, 2,6-pyridinediethanol, 2,6-diacetylpyridine,2,6-bis(chloromethyl)pyridine, 2,6-bis(bromomethyl)pyridine,2,6-pyridinecarbonitrile, quinoline, 2-quinolinecarbonitrile,2-quninolinecarboxaldehyde, 4-quinolinecarbixaldehyde,quinoline-7-carbaldehyde, quninoline-8-methanol, 4-quinolinol,5-quinolinol, 8-quinolinol, and mixture thereof. The most preferredexample is 2,6-dimethylpyridine and 8-quinolinol and2-methy-8-quinolinol.

Lastly, the Mg-based composite support catalyst precursor can beobtained by further contacting the complex containing Si—Ti—N compoundswith the in-situ yielded Mg-based composite support for about 3 to 4hours. Specifically, the magnesium halide composite support is in situprepared by reacting metallic magnesium with an alkyl halide or aromatichalide in the presence of the complex containing Si—Ti—N compounds at atemperature of about 75° C. to 90° C., preferably about 75° C. to 80° C.The molar ratio of alkyl or aromatic halide to metallic magnesium isabout 1.0 to 3.5, preferably about 1.2 to 2.0. The ratio of the complexcontaining Si—Ti—N compounds to metallic magnesium is about 0.01 to 1.5,and preferably about 0.05 to 0.5. Any type of magnesium powder may beused as the metallic magnesium source. Suitable alkyl or aromatichalides have the formula R⁵X wherein R⁵ is an alkyl group typicallycontaining 3 to 20 carbon atoms or an aromatic group typicallycontaining 6 to 18 carbon atoms and X is a halogen, typically chlorineor bromine. Examples of alkyl or aromatic halides include, but are notlimited to, butyl chloride and chlorobenzene.

The magnesium/titanium-based catalyst precursor is prepared in anon-polar solvent. Suitable non-polar solvents are materials in whichall of the reactants used herein, e.g., the silicon compound, thetransition metal compound, and electron donors, are at least partiallysoluble and in liquid state at reaction temperatures. Preferrednon-polar solvents are saturated hydrocarbons and include, but a rotlimited to, alkanes, such as iso-pentane, hexane, heptane, octane, anddecane. A nitrogen atmosphere may be used to prevent exposure to air.The catalyst precursor may be stored in a slurry state under nitrogenfor further pre-polymerization or dried into powder for furtherpre-polymerization or gas phase polymerization.

The catalyst precursor described above contains Ti, Mg, Si, halogen andnitrogen elements, has good morphology and narrow particle sizedistribution and unique flowability. The catalyst precursor is thenactivated by cocatalyst to form the catalyst system of the presentinvention.

Cocatalyst and its Composition

The cocatalyst of the present invention are aluminum compoundsincluding, but not limited to, dimethyl aluminum chloride (DMAC),diethyl aluminum chloride (DEAC), diisobutyl aluminium chloride, ethylaluminum dichloride (EADC), ethylaluminium sesquichloride (EASC), methylaluminum dichloride, triethylaluminium (TEAL), and alkylaluminoxane ormixtures therefrom, or an organohalogenous aluminum compound in-situprepared by reacting alkyl aluminum and/or alkylaluminoxane withhalogenated alkylaluminum compounds.

Alkylaluminoxane, such as methylaluminoxane (MAO), have been widely usedto activate metallocene catalysts or single-site catalysts for producingm-LLDPE, but have not been employed to activate Ziegler-Natta catalystin the prior art. Rather, halogenated alkylaluminum compounds includingDMAC, DEAC, EADC, and EASC have been used to activate Ziegler-Nattacatalyst. As is well known in the art, when using halogenatedalkylaluminum compounds as cocatalyst, Ziegler-Natta catalystsdemonstrate very low activity. When using a combination of halogenatedalkylaluminum compound, such as EADC and triethyl aluminum (TEAL) asdescribed in U.S. Pat. Nos. 6,043,326 and 8,546,499, it was found thatSiO₂-based Ziegler-Natta catalysts have good activity, improved shortchain branching distribution, and reduced soluble extraction. However,the prior art fails to address the processability and melt strength,physical properties (dart impact and tear strengths), and opticalproperties (haze, clarity and gloss) of the product. More importantly,when using a combination of halogenated alkylaluminum compound such asEADC and triethyl aluminum (TEAL) in the present invention, it wasdiscovered that the composition of ethylene/alpha-olefins copolymer orlinear low density polyethylene is much different from that reported inU.S. Pat. Nos. 6,043,326 and 8,546,499, according to analysis fromCRYSTA and TREF techniques. Moreover, the Ziegler-Natta catalyzedethylene/alpha-olefins copolymer of the present invention has sporadiclong chain branches and reversed comonomer composition distribution orshort chain branching distribution (SCBD) in the low-soluble fraction atelution temperature of 30° C. and high molecular weight tail (fraction)obtained from an elution temperature range from about 100° C. to 130° C.The composition of ethylene/alpha-olefins copolymer or linear lowdensity polyethylene provided in this invention is also substantiallydifferent from that reported in assignee's prior patents, such as U.S.Pat. Nos. 8,993,693, and 9,487,608.

Preferred cocatalysts of the present invention are EASC or EADC or DEAC,which can be used alone as a pure cocatalyst or more preferably incombination with triethyl aluminium (TEAL) and/or methylaluminoxane(MAO).

If triethyl aluminium (TEAL) and/or methylaluminoxane (MAO) are used incombination with EASC or EADC or DEAC, it is believed anorganohalogenous compound may be in-situ produced by reacting alkylaluminium or alkylaluminoxane with halogenated alkylaluminum compounds,which is used as cocatalyst in Ziegler-Natta catalysts, thecorresponding polymer prepared has a sporadic long chain branches inhigh molecular weight fractions and a high molecular weight tail alongwith reversed comonomer composition distribution for improvingprocessability, melt strength and optical properties.

When alkylaluminoxane is mixed with halogenated alkylaluminum, it isgenerally believed that a typical reaction to produce theorganohalogenous aluminum compound as cocatalysts is described in thefollowing equation:

wherein the alkylalumoxane may be oligomeric linear and/or cyclicalkylaluminoxanes, R⁶ is C₁-C₂₀ hydrocarbyl, which for present purposesincludes both unsubstituted and substituted species, includingsubstituted species with halogen, alkoxide and hydride, and x is 1-40,preferably about 3-20. The representative example of alkylaluminoxane isselected from methylalumoxane, modified methylalumoxane,tetraethyldialumoxane, tetrabutylalumoxane, bis(diisobutylaluminum)oxide, ethylalumoxane, isobutylalumoxane, polymethylalumoxane, andmixtures or combinations thereof. The alkylaluminoxane is preferablymodified methylalumoxane.

R⁷ is C₁-C₂₀ hydrocarbyl, which for present purposes includes bothunsubstituted and substituted species, including substituted specieswith halogen, alkoxide and hydride; n is typically 0.05 to 20,preferably 0.5 to 2. The mixing temperature between the alkyalumoxaneand alkylaluminium dichloride is typically from about −10° C. to 85° C.,and preferably from about 20° C. to 60° C. The suitable alkylaluminumdihalides include, but is not limited to, methylaluminum dichloride,ethylaluminum dichloride, isobutylaluminum dichloride, isobutylaluminumdichloride, t-butylaluminum dichloride and amylaluminum dichloride, andethylaluminum dichloride. The preferred alkylaluminum dihalide isethylaluminium sesquichloride.

The alkylaluminum dihalide may be prepared in situ via the reactionbetween aluminum trihalide and dialkylaluminum halide. The suitablealuminum trihalide includes, but is not limited to, aluminumtrichloride, aluminum tribromide and aluminum triiodide. Aluminumtrichloride is the preferred aluminum trihalide. Suitable examples ofdialkylaluminum are dimethylaluminum chloride, diethylaluminiumchloride, diisobutylaluminum chloride, di(t-butyl)aluminum chloride, anddiamylaluminum chloride. Diethylaluminum chloride is the preferreddimethylaluminum chloride.

The alkylaluminum dihalide may also be prepared in situ via the reactionbetween alkene and dihaloaluminum hydride. A suitable dihaloaluminumhydride is selected from dichloroaluminum hydride, dibromoaluminumhydride, and diiodoalumminum hydride, preferably dichloroaluminumhydride. Examples of alkenes include 1 to 20 alkyl group with or withoutsubstitute species of halogen, alkoxide and hydride.

The modified methylalumoxane and ethylaluminum dichloride is preferablyused for in-situ preparing the aforementioned organohalogenous aluminumcompounds as cocatalyst. In one embodiment of the present invention, thecocatalysts could be mixed prior to adding to the supported catalystcomponent for activation. In another embodiment, the cocatalysts couldseparately be added to the supported catalyst component for activation.It is particularly advantageous to prepare the organohalogenous aluminumcompounds by reacting the organic aluminum compounds and thecatalytically halogen organic aluminum compounds less than about 2hours, and preferably less than about 1 hour, before starting thecopolymerization. The molar ratio of alkylaluminoxane to halogenatedalkylaluminum compounds is about 0.1 to 3. The preferable ratio of alkylaluminium or alkylaluminoxane to halogenated alkylaluminum compounds isabout 0.5 to 1.5, preferably about a 1:1 ratio.

The supported catalyst precursor is then activated with organohalogenousaluminum compounds as cocatalyst (in-situ produced by reacting alkylaluminium or alkylaluminoxane with halogenated alkylaluminum compounds)to form a catalyst system of the present invention. The cocatalyst istypically used in excess of the transition metal compound. The molarratio of the aluminum in the cocatalyst to the titanium is from about 1to 500 mol/mol, preferably from about 1 to 100 mol/mol, more preferablyfrom about 2 to 50 mol/mol, and most preferably from about 2 to 20mol/mol. The catalyst component may be activated in situ by adding thecocatalyst and catalyst component separately to the polymerizationmedium. It is also possible to combine the catalyst precursor andcocatalyst before their introduction into the polymerization medium, forexample for about 2 hours or less and at a temperature from about −10°C. to 85° C., and preferably from about 20° C. to 60° C. In addition,catalyst component may be activated in situ by adding the cocatalyst andcomponent separately to the polymerization medium in the presence ofethylene to a special prepolymerized catalyst component, which can beused as catalyst composition in the slurry or gas phase polymerizationwith or without additional cocatalysts used thereafter.

Preparation of Ethylene Prepolymer or Prepolymerized Catalyst Component

The supported catalyst precursor, after activation with organohalogenousaluminum compounds (combination of alkyl aluminium or alkylaluminoxanewith halogenated alkylaluminum compounds) may be subjected toprepolymerization in the presence of olefin, and produce an ethyleneprepolymer or prepolymerized catalyst component, which is sequentiallyused for the gas phase polymerization. For example, the solid catalystprecursor and a cocatalyst component, such as an organohalogenousaluminum compound, are contacted with an olefin. Examples of the olefinused for the prepolymerization are ethylene, propylene, 1-butene, and1-hexene. The prepolymerization may be either homopolymerization orcopolymerization. It may be preferable to make a slurry containing thesolid catalyst precursor using a solvent. Examples of suitable solventsinclude aliphatic hydrocarbons such as butane, pentane, hexane, heptane,and aromatic hydrocarbons such as toluene and xylene, preferably hexane.The cocatalyst amount is crucial for the kinetic and reactivity control.The organohalogenous aluminum compound may be used in a ratio of about0.1 to 100, preferably about 0.5 to 50, calculated as the Al/Ti atomicratio, that is, the atomic ratio of the Al atom in the organohalogenousaluminum compound to the Ti atom in the solid catalyst component. Thepreferred ratio is about 2 to 10. Hydrogen is an important factoraffecting the prepolymerization activity and the molecular weight (orMI) control of the ethylene prepolymer. The ratio of hydrogen toethylene may typically be about 0.01 to 10.0, and preferably about 0.05to 1.0. The hydrogen could be charged either at the beginning ofreaction or continually during the reaction. The temperature for theprepolymerization may generally be −30° C. to 100° C., and preferablyfrom −10° C. to 85° C. The prepolymerization temperature is anotherfactor for kinetics and MI control of the ethylene prepolymer. Largetemperature fluctuations during the prepolymerization should be avoided.The temperature fluctuation may typically be controlled within ±5.0° C.,preferably within ±0.5° C. The prepolymerization time relates to theparticle size and the yield of the ethylene prepolymer produced. Theyield and particle size may increase with prolonged prepolymerizationtime. The typical prepolymerization time may be from about 0.5 to 20hours, and preferably from about 1 to 12 hours. The yield of saidethylene prepolymer ranges from about 0.1 to 1000 g per g of said solidcatalyst precursor, and preferably from about 1.0 to 500 g per g of saidsolid catalyst precursor. For gas phase fluidized polymerization, theethylene prepolymer has a yield ranging from about 20 to 160 g per mmolTi of said solid catalyst precursor.

When used for gas phase polymerization, the ethylene prepolymer may becombined with inert diluents to form a slurry, or dried to obtain afree-flowing powder. The drying temperature is typically from about 30°C. to 80° C., and preferably from about 40° C. to 60° C. The averageparticle size of the ethylene prepolymer is typically from about 100 to500 micron, more preferably from about 200 to 300 micron. In addition,small amounts of fine particles (<80 micron) may also be produced. Thetypical fine particle content is from about 2 to 30%, and preferablyfrom about 5 to 12%. High content of fine particles in the ethyleneprepolymer could bring about issues of high static and hot spots, andshould be avoided in the gas phase polymerization. The MI or 12 of theethylene prepolymer is typically from about 0.02 to 100 g/10 min, andpreferably from about 0.5 to 5 g/10 min. The solid powder of theethylene prepolymer can be stored under nitrogen for a relatively longperiod time, typically from about two weeks to a month, and maintaingood activity in the following slurry or gas phase polymerization.

The advantage of using the prepolymer instead of the catalyst precursordirectly for gas phase polymerization includes: a) the improvement inthe morphology of the catalyst with less fine particle content, whichmay increase the particle flowability, inhibit the otherwise dramaticinitial activity, and facilitate the catalyst to be used for gas phasepolymerization in a fluidized bed reactor or stirring bed reactor; b)the ability of tuning the microstructure of the polymer or copolymerproduced, such as comonomer composition distribution, molecular weightdistribution, high molecular weight fraction (tail) and long chainbranching, to the desirable level for tailoring properties of thepolymer product.

Copolymerization of Ethylene and Alpha-Olefin with Ethylene Prepolymeror Prepolymerized Catalyst Component

Ethylene and alpha-olefins may be copolymerized with the ethyleneprepolymer by any suitable process. Such processes includepolymerizations carried out in slurry, in suspension, in solution, or ingas phase. A preferred method for producing LLDPE resins is a gas phaseprocess, including stirred bed reactors and fluidized bed reactors.

Standard polymerization conditions for production of polyolefin polymersby the method of the present invention, such as the polymerizationtemperature, polymerization time, polymerization pressure, monomerconcentration and hydrogen concentration should be selected. Typically,the polymerization temperature should be below the sintering temperatureof polymer particles for gas phase polymerization. For the production ofethylene copolymers, an operating temperature of about 30° C. to 115° C.is acceptable, about 50° C. to 100° C. is preferred, and about 75° C. to95° C. is more preferred. Temperatures of about 75° C. to 90° C. arepreferably used to prepare LLDPE products having a density of 0.90 to0.92 g/mL; temperatures of about 80° C. to 100° C. are preferably usedto prepare LLDPE products having a density of 0.92 to 0.94 g/mL; andtemperatures of about 90° C. to 115° C. are used to prepare LLDPEproducts having a density of 0.94 to 0.96 g/mL. Molecular weight of thepolymers may be suitably controlled with hydrogen when thepolymerization is performed using the catalyst system of the presentinvention described herein. The control of molecular weight may beillustrated by changes in melt indexes (12 and 121) of the polymer.

Copolymerizing the alpha-olefin comonomers with ethylene to achieveabout 1 to 5 mol percent of the comonomer in the copolymer results inthe desired density ranges in the copolymers. The amount of thecomonomer needed to achieve this result will depend on the particularcomonomer(s) employed. It has been found that when using a gas phasecatalytic polymerization reaction, 1-butene, 1-hexene and4-methyl-1-pentene can be incorporated into ethylene-based copolymerchains with high efficiency. A relatively small concentration of1-butene, 1-hexene or 4-methyl-1-pentene in the gas phase reactor canlead to a relatively large incorporation of 1-butene, 1-hexene or4-methyl-1-pentene into the resulting copolymer. For example, 1-butene,1-hexene or 4-methyl-1-pentene in an amount up to about 18 percent byweight, preferably about 2 to 12 percent by weight, may produce LLDPEresins having a density of less than 0.940 g/mL.

LLDPE resins may be copolymers of ethylene with one or more C₃-C₁₀alpha-olefins. Thus, copolymers having two types of monomer units arepossible as well as terpolymers having three types of monomer units.Particular examples of such polymers include, but are not limited to,ethylene/l-butene copolymers, ethylene/l-hexene copolymers,ethylene/4-methyl-1-pentene copolymers, ethylene/propylene/1-buteneterpolymers, ethylene/propylene/1-hexene terpolymers,ethylene/l-butene/1-hexene terpolymers. Particularly preferredcomonomers are 1-hexene, 4-methyl-1-pentene, propylene, 1-butene, andmixtures thereof.

Polymer Characterization

Density was measured according to ASTM D 1505-98. The copolymer producedin accordance with the present invention may have a density of about0.960 g/mL or less, preferably about 0.952 g/mL or less, or morepreferably about 0.940 g/mL or less. In accordance with certain aspectsof the present invention, it is possible to achieve densities of lessthan about 0.910 g/mL and even as low as about 0.870 g/mL. Copolymerresins produced in accordance with the present invention preferablycontain at least about 75 percent by weight of ethylene units.Preferably, the copolymer resins of the present invention contain atleast about 0.5 weight percent, for example, from about 0.5 to 25 weightpercent of an alpha-olefin.

The molecular weight of the copolymers may be controlled in a knownmanner, preferably by using hydrogen. With the catalysts producedaccording to the present invention, molecular weight may be suitablycontrolled with hydrogen when the polymerization is carried out attemperatures from about 20 to 300° C. This control of molecular weightmay be evidenced by a measurable positive change of the melting index(I₂). Melt flow index (MI) of the polymer was measured at 190° C.,according to ASTM D1238. Melt flow ratio (MFR), which is the ratio ofhigh melt flow index (HLMI or I₂₁) to melt index (MI or I₂), was used asmeasure of melt fluidity and a measure of the molecular weightdistribution.

The molecular weight distribution (MWD) of the polymers preparedaccording to the present invention, as expressed by the MFR values,varies from about 10-40. MFR is the ratio of the high-load melt index(HLMI or I₂₁) to the melt index (MI or I₂) for a given resin(MFR=I₂₁/I₂). The ethylene/1-hexene copolymer having a density of about0.910 g/mL to 0.930 g/mL, in a preferred embodiment, has a melt indexratio (I₂₁/I₂) of between about 20 and 30.

Molecular weights and molecular weight distribution were measured by GelPermeation Chromatography (GPC). The polymers of the present inventionhave a molecular weight distribution, a weight average molecular weightto number average molecular weight (M_(w)/M_(n)), of from about 2.5 to80, preferably from about 2.5 to 4.5, more preferably from about 3.0 to4.0, and most preferably from about 3.2 to 3.8. The polymers have aratio (M_(z)/M_(w)) of z-average molecular weight (Mz) to weight averagemolecular weight of greater than about 2.5. In one embodiment, thisratio is from about 2.5 to 3.8. In yet another embodiment, this ratio isfrom about 2.5 to 3.5. The ratio of z-average molecular weight to weightaverage molecular weight (M_(z)/M_(w)) reflects inter- and/orintra-macromolecular entanglement and unique polymer rheologicalbehavior.

Molecular weight measurements were carried out using a high temperaturesize exclusion chromatograph (SEC) (Polymer Char) equipped with adifferential refractive index (DRI) and infrared (IR) (PolyChar, IR4)detectors, a Viscotek model 210R viscometer, and a multi-angle laserlight scattering (MALLS) apparatus (Wyatt, DAWN EOS). All measurementswere taken at 145° C. using 1,2,4-trichlorobenzene (TCB) as the solvent.The system was calibrated with a standard material (NBS 1475) with aweight-average molecular weight of 52000 g/mol and an intrinsicviscosity of 1.01 dL/g. The refractive index increment, dn/dc, wascalculated from the calibrated DRI detector as 0.11 mL/g. Molecularweights for the polyethylene polymers of the present invention werecalculated from the intrinsic viscosity detector using the followingMark-Houwink parameters; K=4.5×10⁻⁴ dL/g and a=0.735, established forlinear polyethylene from a polystyrene calibration.

SEC with the multiple detectors can detect differences between thehydrodynamic volume of linear and branched polymers. Simultaneousmeasurement of intrinsic viscosity [η], and absolute molecular weight,M_(LS), for each fraction of polymer separated by the chromatographycolumns can provide information about the structure of branchedpolymers. Mark-Houwink plots (log[η] vs log[M_(w)]) for each slice ofthe SEC elution, can be used to qualitatively observe branching. Thelinear standard polyethylene polymers behave in a fashion described bythe Mark-Houwink relation: [η]=KM^(a), where K and a can be obtainedfrom the slope and intercept of the Mark-Houwink plot. However, branchedpolymers begin to deviate from linear behavior at high molecularweights, that is, the slopes of the Mark-Houwink plot for the branchedpolymer deviate from that of the linear standard. The deviation fromlinear behavior is subtle at low branch point density but became moreapparent as branch point density is increased. In accordance withcertain teachings of the present invention, this deviation from linearbehavior is observed in the high molecular weight fractions of theinventive samples, that is, the inventive samples have long branchedpolymer chains. In contrast, the comparative samples conform to thelinear relationship of Mark-Houwink plot in all the molecular weightfractions, indicating they do not contain any long chain branching inthe polymers. SCBD data can be obtained using a SEC-FTIR hightemperature heated flow cell (Polymer Laboratories) as reported in theliterature (P. J. DesLauriers, D. C. Rohlfing, and E. T. Hsieh,Quantifying short chain branching microstructures in ethylene 1-olefincopolymers using size exclusion chromatography and Fourier transforminfrared spectroscopy (SEC-FTIR) Polymer, 2002, 43, 159).

Analytical Temperature Rising Elution Fractionation (TREF) technique wascarried out on a PolyChar TREF 200+ instrument, 40 mg of polymer sampleand 20 mL of 1,2,4-trichlorobenzene were sequentially charged into thevessel to dissolve the polymer. Then, an aliquot of the resultingpolymer solution was loaded on the column and cooled at 0.5° C./min to35° C. Afterward, the elution began using a 0.5 mUmin flow rate andheating at 1° C./min up to 140° C.

Comonomer distribution breadth index (CDBI), defined as the weightpercent of the ethylene copolymer having a comonomer content within 50percent of the median total molar comonomer content, can be calculatedby the data obtained from TREF, as described in the literature (L.Wild., T. R. Ryle, D. C. Knobeloch, and I. R. Peat, Determination ofbranching distributions in polyethylene and ethylene copolymers J.Polym. Sci. Polym. Phys. Ed., 1982, 20, 441).

CRYSTAF is a fully automated instrument intended for the fastmeasurement of the Chemical Composition Distribution (CCD) inPolyolefins. CRYSTAF instrument performs the Crystallization AnalysisFractionation technique to separate the polymer by its comonomercontent. The polymer is initially dissolved in an appropriate solvent atan increased temperature, and then the temperature of solution isreduced very slowly resulting in gradual crystallization of the polymer.The process is done in a single temperature ramp (crystallization step),while the polymer solution concentration is monitored by using theInfrared Detector IR4 of Polymer Char. CRYSTAF can be converted into aCRYSTAF-TREF combined system capable of running both techniques by usingthe same hardware. Each technique can provide complementary informationon the CCD in some complex resins.

Copolymer Compounding/Extrusion and LLDPE Pellets

The copolymers produced in accordance with the present invention mayalso be blended with additives to form compositions that can then beused in articles of manufacture. Those additives include antioxidants,nucleating agents, acid scavengers, plasticizers, stabilizers,anticorrosion agents, blowing agents, other ultraviolet light absorberssuch as chain-breaking antioxidants, etc., quenchers, antistatic agents,slip agents, pigments, dyes and fillers and cure agents such asperoxide. These and other common additives in the polyolefin industrymay be present in polyolefin compositions from about 0.01 to 50 wt % inone embodiment, and from about 0.1 to 20 wt % in another embodiment, andfrom about 1 to 5 wt % in yet another embodiment.

In particular, antioxidants and stabilizers such as organic phosphitesand phenolic antioxidants may be present in the polyolefin compositionsfrom about 0.001 to 5 wt % in one embodiment, and from about 0.02 to 0.5wt % in yet another embodiment. Non-limiting examples of organicphosphites that are suitable includetris(2,4-di-tert-butylphenyl)phosphite (IRGAFOS 168) and tris(nonylphenyl)phosphite (WESTON 399). Non-limiting examples of phenolicantioxidants include octadecyl 3,5-di-t-butyl-4-hydroxyhydrocinnamate(IRGANOX 1076) and pentaerythrityltetratris(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (IRGANOX 1010);and 1,3,5-tri(3,5-di-tert-butyl-4-hydroxybenzyl-isocyanurate (IRGANOX3114).

Fillers and fatty acid salts may also be present in the polyolefinincluding LLDPE composition. Filler may be present from about 0.1 to 65wt % in one embodiment, and from about 0.1 to 45 wt % of the compositionin another embodiment, and from about 0.2 to 25 wt % in yet anotherembodiment. Desirable fillers include, but are not limited to, titaniumdioxide, silicon carbide, silica (and other oxides of silica,precipitated or not), antimony oxide, lead carbonate, zinc white,lithopone, zircon, corundum, spinel, apatite, Barytes powder, bariumsulfate, magnesiter, carbon black, dolomite, calcium carbonate, talc andhydrotalcite compounds of the ions Mg, Ca, or Zn with Al, Cr or Fe andCO₃ ⁻ and/or HPO₄, hydrated or not; quartz powder, hydrochloricmagnesium carbonate, glass fibers, clays, alumina, and other metaloxides and carbonates, metal hydroxides, chrome, phosphorous andbrominated flame retardants, antimony trioxide, silica, silicone, andblends thereof. These fillers may particularly include any other fillersand porous fillers and supports known in the art.

Fatty acid salts may be present from about 0.001 to 6 wt % of thecomposition in one embodiment, and from about 0.01 to 2 wt % in anotherembodiment. Examples of fatty acid metal salts include lauric acid,stearic acid, succinic acid, stearyl lactic acid, lactic acid, phthalicacid, benzoic acid, hydroxystearic acid, ricinoleic acid, naphthenicacid, oleic acid, palmitic acid, and erucic acid, suitable metalsincluding Li, Na, Mg, Ca Sr, Ba, Zn, Cd, Al, Sn, Pb and so forth.Preferred fatty acid salts include magnesium stearate, calcium stearate,sodium stearate, zinc stearate, calcium oleate, zinc oleate, andmagnesium oleate.

In the physical process of producing the blend of polyolefin and one ormore additives, sufficient mixing should take place to assure that auniform blend will be produced prior to conversion into a finishedproduct. The polyolefin can be in any physical form when used to blendwith the one or more additives. In one embodiment, reactor granules,defined as the granules of polymer that are isolated from thepolymerization reactor, are used to blend with the additives. Thereactor granules have an average diameter of from about 10 μm to 5 mmand from about 50 μm to 10 mm in another embodiment. Alternately, thepolyolefin is in the form of pellets, such as, for example, having anaverage diameter of from 1 mm to 6 mm that are formed from meltextrusion of the reactor granules.

One method of blending the additives with the polyolefin is to contactthe components in a tumbler or other physical blending means, thepolyolefin being in the form of reactor granules. This can then befollowed, if desired, by melt blending in an extruder. Another method ofblending the components is to melt blend the polyolefin pellets with theadditives directly in an extruder, Brabender or any other melt blendingmeans.

Rheological tests were carried out on compression molded disk of thepolymer pellets in an ARES-G2 Rheometer (TA Instrument) using parallelplate geometry. Small strain (3%) dynamic mechanical experiments wereperformed at 190° C. in a nitrogen atmosphere. The resulting complexviscosity as a function of imposed oscillatory frequency (|η*| vs. ω)was then curve fitted with modified three parameter Carreau-Yasuda (CY)empirical model:

|η*(ω)|=η_(o)/[1+(τ_(η)ω)^(a)]^((1-n)/a),

to obtain the zero shear viscosity (η_(o)), characteristic viscousrelaxation time (τ_(n)) and the breadth parameter (a). Due to thelimitation of the measurement range, n is taken as 0.1818 based ontheoretical value. (Graessley W. W. Viscosity of Entangling PolydispersePolymer, J. Chem. Phys. 1967, 47, 1942-1953)

The Janzen-Colby model was used for characterizing the long chainbranching effect on polymer melt viscosity (J. Janzen and R. H. Colby,Diagnosing long-chain branching in polyethylenes, Journal of MolecularStructure 1999, 485-486, 569-584). The long chain branch content(vertexes per a million carbons) was denoted as J-C α value. For thecases with polymer dispersity of >2.0, a small correction based on Yau'sarticle (Wallace W. Yau, A rheology theory and method on polydispersityand polymer long-chain branching, Polymer 2007, 48, 2362-2370) was alsorequired to offset the effect of molecular weight breadth.

The date of storage modulus (G′) and loss modulus (G″) as a function ofshear rate (γ) can also be obtained using Cox-Merz rule. Melt strengthindex (MSI), defined as the ratio of storage modulus and loss modulus(G′/G″) at a shear rate of 0.03 s⁻¹, is used as an empirical parameterfor evaluating melt quality in the film blowing process. In accordancewith the present invention, MSI value is between about 0.01 and 0.80.

Film Extrusion and Film Properties

The polymers produced according to the present invention are more easilyextruded into film products by cast or blown film processing techniquesas compared to commercial octene-1 LLDPE and commercial mLLDPE (I) withcomparable melt index and density. The resins in this invention have,for a comparable MI, a MWD narrower than 1-hexene copolymer resins butbroader than mLLDPEs. The resins made from this invention also exhibit amolecular structure, such as comonomer composition distribution, similarto typical mLLDPE resins.

More specifically, in the present invention, the compounded polymerresins are extruded through a single screw laboratory extruder and blowninto film under the following conditions: BUR=2.5:1, gauge=1 mil, melttemperature=425° F. Film dart impact (g/mil) was tested by ASTM D-1709,and film Elmendorf Tear (g/mil) by ASTM D-1922 and secant modulus byASTM D-882, film haze by ASTM D-1003, film clarity by ASTM D-1746, andgloss by ASTM D-2457.

EXAMPLES

In order to provide a better understanding of the foregoing discussion,the following non-limiting examples are offered. Although the examplesmay be directed to specific embodiments, they are not to be viewed aslimiting the invention in any specific respects.

Catalyst Preparation

(a) Preparation of Catalyst Precursor

Catalyst precursor was synthesized as described in U.S. Pat. No.7,618,913, adapted to the present invention as follows:

Anhydrous hexane (2 L), magnesium (31.9 g), iodine (3.3 g),2-methyl-1-propanol (5.0 mL), titanium propoxide (7.2 mL) and butylchloride (5.0 mL) were successively charged into a 5 L reactor equippedwith an anchor stirrer driven by a magnetic motor. The reactor washeated to 85° C. within 45 minutes and then cooled to 80° C. within 30minutes. Tetraethoxy orthosilicate (20 mL) and silicon tetrachloride (38mL) were added to the reactor and held at 80° C. for 40 minutes to yielda yellow-brown reaction product in the suspension. Next, titaniumpropoxide (38.9 mL) and TiCl₄ (18.3 mL) were charged to the suspensionat 80° C., and the slurry mixture was stirred for 0.5 hour to yieldorganic silicon complex containing titanium, followed by the slowintroduction of 2,5-dimethylpyridine (20.0 mL) in the suspension. Thenn-butyl chloride (230 mL) was added at the rate of 0.96 mL/min and heldfor 4 hours. The reaction was continuously stirred at 80° C. for 3 hourto yield a brown/yellow reaction product. The suspension was cooled to50° C., resulting in a brownish precipitate, which was subsequentlywashed 3 times with 2 L hexane at 50° C. Drying the precipitate led to asolid magnesium-based supported titanium catalyst precursor. Analysisshows that the supported catalyst precursor composition contains 7.5 wt% Ti, together with composition of Si, Mg, Cl, and N elements.

(b) Preparation of Ethylene Prepolymer or Prepolymerized CatalystComponent

A typical process for preparing prepolymer is as follows: Two liters ofn-hexane, 60 mmoles of EADC (or EASC), 60 mmol MAO (or TEAL) and aquantity of the catalyst precursors containing 12.6 mmoles of titaniumwere subsequently introduced into a 5 liter stainless steel reactorunder nitrogen atmosphere, provided with a stirring device rotating at750 rpm and heated to 68° C. Hydrogen was then introduced to obtain apartial pressure of 0.5 bar, and ethylene was introduced at a steadyflow rate of 160 g/h for 1-3 hours. Subsequently, the reactor wasdegassed and its contents were transferred into a flask evaporated inwhich the hexane was removed under vacuum followed by nitrogen heatingto 40-50° C. After evaporation, 160-480 g of prepolymer containing40-120 g polyethylene per mmoles of titanium was obtained as an ethyleneprepolymer (based on polymerization process). The prepolymer was storedunder nitrogen and would be used for the sequential slurry or gas phasepolymerization.

(c) Gas Phase Copolymerization of Ethylene and 1-Hexene

Catalyst precursor is directly charged to slurry or gas phasepolymerization reactor, together with the cocatalyst, a halogenatedaluminium alkyl or organohalogenous aluminum compounds prepared in-situby reacting alkyl aluminium and/or alkylaluminoxane with halogenatedalkylaluminum compound. Catalyst precursor was in-situ activated andthen used for copolymerization of ethylene with alpha-olefins including1-hexene.

Alternatively, catalyst precursor is activated first with thecocatalyst, a halogenated aluminium alkyl or organohalogenous aluminumcompounds, in the presence of ethylene and hydrogen to produceprepolymerized catalyst component (or prepolymer) with approximateparticle size (as described above). The prepolymerized catalystcomponent (or prepolymer) then is directly used in slurry or gas phasepolymerization without additional cocatalyst thereafter forcopolymerization of ethylene with alpha-olefins.

With reference to Table 1, Examples 1-6 are ethylene/1-hexene copolymersproduced by using lab-scaled gas phase reactor in accordance with thefollowing general procedure. Co-polymerization was carried out in anautoclave designed for stirred gas phase polymerization, equipped withan anchor stirrer with magnetic stirrer drive above the top of autoclaveand a valve at the base of the autoclave to withdraw polymer. Thetemperature was regulated using steam/water via the outer jacket of theautoclave. A fluidized seed particle of polymer (400 g) and 60 g of theethylene prepolymer previously prepared in (b) were introduced into thegas phase polymerization reactor under nitrogen atmosphere, providedwith a stirring device rotating at 150 rpm and heated to 60° C. Nitrogenand hydrogen were charged into the reactor to provide total pressure of3-5 bars and a given ratio of hydrogen and ethylene (P_(H2)/P_(C2))partial pressure. After the reactor temperature was raised to 85° C.,ethylene (5-7 bars) was charged into the reactor to obtain totalpressure of 10 bars, together with 1-hexene (C₆) at a given C₆/C₂ molarratio. The copolymerization was maintained at 85° C. The feed of C₆/C₂was continued at a given C₆/C₂ molar ratio until 1000 g of ethylene wasconsumed during the gas phase polymerization. The reactor was thencooled down and degassed and an ethylene/1-hexene polymer free fromagglomerate was drawn off. The polymer was collected for property tests.

Examples 7 and 8 are ethylene/1-hexene copolymers produced by usingcommercial gas phase process in accordance with the following generalprocedure. Polymerization was conducted in a commercial BP processfluidized bed gas phase reactor operating at approximate 300 psig totalpressure. Fluidizing gas was passed through the bed at a velocity ofapproximate 1.8 feet per second. The fluidizing gas exiting the bedentered a resin disengaging zone located at the upper portion of thereactor. The fluidizing gas the entered a recycle loop and passedthrough a cycle gas compressor and water-cooled heat exchanger. Theshell side water temperature was adjusted to maintain the reactiontemperature to the specified value in the range of from 175° F. to 195°F. Ethylene, hydrogen, 1-hexene, and nitrogen were fed to the cycle gasloop just upstream of the compressor at quantities sufficient tomaintain the desired gas composition. Gas compositions were measured byan on-line GC analyzer. The catalyst in the form of prepolymer preparedin (b), with a mixed cocatalyst from a 1:1 to 1:1.5 ratio of TEAL toEADC in Example 7 and Example 8, respectively, was injected to thereactor bed through a stainless steel injection tube at a ratesufficient to maintain the desired polymer production rate. Nitrogen gaswas used to disperse the catalyst into the reactor. Product waswithdrawn from the reactor, polymer was collected after discharging anddegassing in the downstream, gases were recycled in the loops andresidual catalyst and cocatalyst in the resin was deactivated with a wetnitrogen purge. Final powder product (polymer) was transferred intoextrusion and pelletized into granular product.

Comparative Examples 1-3 is ethylene/1-hexene copolymer or linear lowdensity polyethylene prepared in the same manner as described inExamples 1-6 except that cocatalysts used are TEAL, TnOA, and MAO,respectively.

Comparative Example 4 is commercial super-hexene resin. ComparativeExample 5 is commercial 1-octene/ethylene LLDPE resin (C8-LLDPE).Comparative Example 6 is commercial metallocene ethylene-1-hexenecopolymer resin (m-LLDPE). Comparative Example 7 is commercial LLDPEprepared by BP fluidized gas phase process in the same manner asdescribed in Example 7 except that prepolymerized catalyst or prepolymeris prepared with TnOA cocatalyst (without a halogenated aluminium alkylor organohalogenous aluminum compounds).

Granular products for Examples 1-8 and Comparative Examples 1-3, and 7were screened and dry-blended with suitable additives such asIrganox-1076, TNPP, Eurmide, Zinc stearate, and Polybloc Talc.Pelletizing of Examples 1-7 and Comparative Examples 1-2, and 7 wascarried out on a twin-screw extruder equipped with an underwaterpelletizer, with melt temperature of 420-445° F.

Table 1 shows the results of ethylene/1-hexene copolymerization withcatalyst prepared as described under Examples a) and cocatalyst TEAL orTnOA or a halogenated aluminium alkyl compounds such as TEAJLEADCmixture or MAO/EADC mixture. The commercial 1-octene/ethylene LLDPEresin and commercial metallocene ethylene-1-hexene copolymer resin(m-LLDPE) is used for comparison.

Combination of catalyst with TEAL, TnOA, TEAL/EADC mixture, and MAO/EADCmixture cocatalyst produced polymer powder with high bulk density. Thepolymers showed a quite good bulk density of over 0.35 g/ml. However,catalyst system with TEAL cocatalyst showed low activity and high staticin the gas phase reactor, which results in reactor fouling. Catalystsystem with EADC cocatalyst has very low activity, which cannot beoperative in gas phase reactor to produce polymer.

Table 1 compares the properties of polymers from different cocatalysts.FIG. 1 and FIG. 2 compares the rheological behavior of polymers preparedby advanced Ziegler-Natta catalyst with different cocatalysts TEA/EADCmixture vs. TEAL, and TEA/EADC vs. TnOA, respectively. Obviously theinventive examples prepared with cocatalyst TEA/EADC mixture or MAO/EADCmixture show improved shear shinning behavior and higher melt strengthindex (MSI), which can further enhance processability and increaseextrusion rate. FIG. 3 and FIG. 4 compares the GPC curves of polymersfrom different cocatalysts. The inventive examples from a halogenatedaluminum alkyl compounds as cocatalyst such as TEAL/EADC mixture orMAO/EADC mixture show high molecular weight tail and high M_(z)/M_(w)ratio, as compared to the comparative examples from TnOA, TEAL, andcommercial ZN-based C2/C8 LLDPE and commercial m-LLDPE.

The inventive polymers prepared by the combination of above-mentionedcatalyst with a halogenated aluminum alkyl compounds as cocatalyst suchas TEA/EADC mixture or MMAO/EADC mixture have sporadic long chainbranches in high molecular weight portion. By contrast, the comparativeexamples from TnOA, TEAL, and commercial ZN-based C₈-LLDPE andcommercial m-LLDPE do not show any long chain branches, even at highmolecular weight portions (FIG. 5 and FIG. 6). Also, there is nosporadic long chain branches contained in the polymer reported in U.S.Pat. Nos. 6,043,326 and 8,546,499 by using a mixed cocatalyst ofTEAL/EADC or TEA/DEAC. The curves of log(IV) vs log M for the inventivesamples show linear relationship at moderate molecular weight fractions(<300,000 g/mol), but deviate linear relationship at high molecularweight fractions because the long chain branches occurring in very longpolymer chains reduce gyration of radius. In contrast, the curve oflog(IV) vs log M for the comparative examples show linear relationshipin all the measurement range of molecular weight fractions, indicatingthe polymer chains are linear and free of long chain branches. The longchain branches account for the optical properties and processabilityimprovement of the inventive polymers. As expected, a low level of longchain branches was obtained with less than 1 per 10⁶ total carbon atomsin the polymer composition to maintain excellent physical properties(such as dart impact resistance and MD tear strength), but to improvepolymer processability.

From Table 1 and Table 2 it can be seen that the inventive polymerprepared in commercial BP process gas phase reactor has novel polymercomposition, wherein polymer has unique rheology behavior (higher MSI),and long chain branching structure (defined as JC-a), which improve theextrusion processability and film optical properties (haze % andclarity). Therefore, as compared to polymer composition (with TnOAcocatalyst) reported in Assignee's prior U.S. Pat. Nos. 8,993,693, and9,487,608, the inventive polymer prepared with a halogenated aluminumalkyl compounds as cocatalyst such as TEA/EADC mixture has the improvedmelt strength (even better than comparable to commercial C8-LLDPE), andexcellent optical properties on par with commercial m-LLDPE andcommercial C8-LLDPE.

TREF curves of the ethylene/1-hexene copolymers produced with thecatalyst and cocatalyst a halogenated aluminum alkyl compounds such asTEA/EADC mixture or MMAO/EADC mixture were compared to TREF curves ofthe copolymers obtained with TEAL or TnOA as cocatalyst by integratingthe elution areas according to elution temperature (Table 3).

The results from Table 3 demonstrate clearly that there was a decreasein the short chain branching comonomer fraction (very low densityfraction) eluted below 30° C. or 40° C., and a corresponding increase inthe comonomer fraction eluted between 60° C. and 94° C., which indicatesa good chemical composition distribution (CCD) when the mixed cocatalystwas used. Moreover, when using mixed catalyst containing a halogenatedaluminum alkyl compound, the fraction eluted between 94° C. and 102° C.also decrease, while new fraction eluted over 102° C. was obtained tobalance physical properties. Overall, the new polymer composition in theinvention is different from that reported in Assignee's prior U.S. Pat.Nos. 8,993,693, and 9,487,608 by using TnOA as cocatalyst, and alsodifferent from composition reported in U.S. Pat. Nos. 6,043,326 and8,546,499 by using a mixed cocatalyst from a 1:1 mixture of TEAL/EADC orTEA/DEAC.

Table 4 lists average weight molecular weight (Mw) of each fractioneluted from temperatures of 30-102° C. When the mixed cocatalystcontaining a halogenated aluminum alkyl compound was used, The M_(w) ofall fractions is obviously increased. In particular, fraction containinghigher short chain branching commoner (very low density fraction) elutedbelow 35° C. has high molecular weight of over 100,000 g/mol similar toother fractions eluted from temperatures from 35-94° C., and fractioneluted at 100° C. or higher (at least 5.0 wt % of a crystallizingpolymer component) has very high molecular weight of over 150,000 g/mol.This is one of reasons that new polymer composition in the invention hasimproved mechanical properties (Table 5).

Short chain branching distribution of all fractions eluted from thetemperatures of 20-130° C. was measured by GPC-FTIR. (FIG. 7a -FIG. 7d). From these GPC-FTIR results it can be clearly seen that polymercomposition in the invention has a substantially constant distributionof short chain branching profile across its molecular weightdistribution (MWD) in each fraction over elution temperature range from30° C. to 94° C., indicating very homogeneous comonomer compositiondistribution as a function of molecular weight, especially in thefraction eluted at 35° C. As compared to TnOA cocatalyst reported inAssignee's prior U.S. Pat. Nos. 8,993,693, and 9,487,608, when using amixed cocatalyst containing a halogenated aluminum alkyl compound, ahigh molecular weight tail in the fractions over elution temperaturerange from 100° C. to 130° C. was achieved, and fractions with a highmolecular weight tail demonstrated a reversed distribution of comonomercomposition profile across the molecular weight distribution.

The unique polymer structure of the present invention provides it withadvantages in certain properties over other comparative polymers. Asshown in Table 5, the inventive resin from TEAL/EADC, MAO/EADC (incombination with advanced Ziegler-Natta catalysts disclosed) has asuperior balance of physical properties and optical properties. Comparedto the resin from TnOA or TEAL, the inventive resins show enhancedprocessability (even better than commercial C8-LLDPE), and improvedoptical properties (low haze, high clarity and high gloss) on par withthose of C8-LLDPE and mLLDPE polymers, while it still maintainsexcellent MD tear strength, outstanding toughness (e.g. dart impact),and stiffness (secant modulus at 1% strain).

As such, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered ormodified and all such variations are considered within the scope andspirit of the present invention. Whenever a numerical range with a lowerlimit and an upper limit is disclosed, any number falling within therange is specifically disclosed. Moreover, the indefinite articles “a”or “an”, as used in the claims, are defined herein to mean one or morethan one of the element that it introduces.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Cocatalyst TEAL/EADC TEAL/EADC TEAL/EADC TEAL/EADC MAO/EADC MAO/EADCTEAL/EADC ratio 1:1 1:1 1:1 1.2:1 1:1 1.2:1 MI, g/10 min 0.89 0.95 0.900.96 0.85 0.67 Bulk Density, g/ml 0.365 0.371 0.385 0.361 0.382 0.385Resin Density, g/ml 0.9181 0.9197 0.9205 0.9181 0.9181 0.9188 Mw/Mn 4.54.5 4.4 4.4 4.4 4.5 Mz/Mw 3.9 3.9 3.5 3.7 3.9 4.2 Tm, ° C. 124.5 124.9125.3 124.4 124.2 124.1 MSI 0.21 0.19 0.18 0.18 0.35 0.33 JC-α 0.30 0.260.27 0.13 0.65 0.60 Comparative Comparative Comparative ComparativeComparative Comparative Example 1 Example 2 Example 3 Example 4 Example5 Example 6 Cocatalyst TEAL TnOA MAO Super-hexene C8-LLDPE m-LLDPETEAL/EADC ratio MI, g/10 min 0.90 0.80 0.80 0.95 0.98 0.96 Bulk Density,g/ml 0.360 0.351 0.365 — — — Resin Density, g/ml 0.9205 0.9198 0.92070.9215 0.9215 0.9206 Mw/Mn 3.7 3.6 3.7 3.8 4.1 2.6 Mz/Mw 2.8 2.9 2.9 2.83.2 1.9 Tm, ° C. 124.5 124.7 124.2 123.5 121.4 118.0 MSI 0.08 0.10 0.090.08 0.10 0.02 JC-α 0 0 0 0 0 0

TABLE 2 Comparative Comparative Inventive Inventive Comparative Example5 Example 6 Sample Example 7 Example 8 Example 7 (C8-LLDPE) (m-LLDPE)Cocatalyst TEAL/EADC TEAL/EADC TnOA — MAO TEAL/EADC Ratio 1:1 1.5:1 — —— H2/C2 ratio 0.325 0.241 0.245 — — MI (g/10 min) 0.73 0.71 0.84 0.960.96 Density (g/mL) 0.9221 0.9214 0.9218 0.9262 0.9213 M_(w)/M_(n) 4.34.2 3.7 4.0 2.9 M_(z)/M_(w) 3.29 3.29 2.63 3.07 1.89 T_(m) (° C.) 125125 125 122 119 MSI 0.18 0.17 0.10 0.10 0.02 JC-α 0.20 0.18 0 0 0 Haze(%) 11.0 12.1 22.0 11.2 11.5 Clarity (%) 92.0 92.4 83.5 92.3 92.8

TABLE 3 Fraction Fraction Fraction Fraction Fraction Fraction Density,<30° C. ≤40° C. 30-60° C. 60-94° C. >94 >100° C. Cocatlyst Example g/cc(wt %) (wt %) (wt %) (wt %) (wt %) (wt %) TEAL Comparative 0.9160 25.527.5 6.0 23.5 45.0 0 Example 1 TnOA Comparative 0.9162 19.4 21.4 6.237.6 36.8 0 Example 2 0.9160 18.8 20.7 6.6 37.2 37.4 0 TEAL/EADC Example1 0.9160 16.5 17.1 11.1 42.5 29.9 5.5 Example 2 0.9180 14.8 16.2 10.545.5 29.2 5.0 Example 3 0.9200 13.5 15.1 10.1 44.1 33.7 5.5 Example 40.9161 15.1 17.5 10.5 44.5 29.9 5.5 MAO/EADC Example 5 0.9159 15.9 17.813.5 44.6 28.0 6.5 Example 6 0.9161 14.5 16.7 13.2 45.0 27.3 6.2

TABLE 4 Samples Compara- Compara- tive tive Example 1 Example 5 Example1 Example 2 TEAL/ MAO/ TEAL TnOA EADC (1:1) EADC (1:1) GPC M_(w) GPCM_(w) GPC M_(w) GPC M_(w) Fraction <35° C. 21,914 93,098 102,019 105,359Fraction 35-60° C. 91,510 99,100 99,124 98,639 Fraction 60-94° C.133,149 120,808 120,583 124,534 Fraction 94-100° C. 138,595 138,913132,570 130,108 Fraction >100° C. nil nil 163105 163,927

TABLE 5 Comparative Comparative Comparative Comparative Example 1Example 3 Example 6 Example 2 Example 4 Example 5 Example 6 CocatalystTEAL/EADC TEAL/EADC MAO/EADC TnOA Super-hexene C8-LLDPE m-LLDPETEAL/EADC Ratio 1:1 1:1 1.2:1 — — — — Film Gauge Target (mils) 1.00 1.001.00 1.00 1.00 1.00 1.00 Blow-up Ratio (BUR) 2.5 to 1 2.5 to 1 2.5 to 12.5 to 1 2.5 to 1 2.5 to 1 2.5 to 1 TEAR STRENGTH 465 497 454 506 413342 241 MD, g/mil TEAR STRENGTH 578 564 561 647 712 663 581 TD, g/milDART IMPACT, g/mil 555 544 589 658 293 270 924 Film HAZE, % 11 12 8 2227 11 11 Film Clarity, % 92 90 92 84 82 92 93 Film Gloss, 45° 74 73 8056 46 74 73 Tensile Str. @ Brk (MD), 5443 5456 4494 5639 5395 3863 3122psi Tensile Str. @ Brk (TD), 4776 4369 3969 4960 4347 2760 3094 psi FilmElongation @ Brk 643 711 652 672 591 652 534 (MD) % Film Elongation @Brk 774 783 632 884 715 865 546 (TD) % (MD) SEC. MOD @ 17890 18592 1728818156 18693 18311 18027 % STRN, % (TD) SEC. MOD @ 20223 19356 1963519549 19837 18994 17910 % STRN. %

What is claimed is:
 1. A Ziegler-Natta catalyzed ethylene/alpha-olefinscopolymer, wherein the copolymer comprises the following properties:density of between 0.890 and 0.935 g/cc; C4-C10 comonomer content ofbetween 1 and 20 wt %; melt index (I2) of between 0.5 and 10 dg/min;ratio (M_(z)/M_(w)) of z-average molecular weight (Mz) to weight averagemolecular weight (Mw) of between 3.0 and 10; melting point over 124° C.across the density of 0.890 to 0.935 g/cc; sporadic long chain brancheswith J-C α value of less than 5; melt strength index, defined as theratio of storage modulus to loss modulus (G′/G″) at a shear rate of 0.03s⁻¹, is less than 5; weight average molecular weight Mw of less than200,000 g/mol; a fraction soluble below about 30° C. of greater than 12wt %, determined by CRYSTAF, having a weight average molecular weight Mwof higher than 90,000 g/mol, determined by gel permeation chromatography(GPC); a fraction soluble between about 60° C. and 75° C. of less than35 wt %, determined by CRYSTAF; greater than 13.5 wt % of a polymercomponent having an elution temperature below about 30° C., determinedby temperature rising elution fractionation (TREF) analysis; greaterthan 15 wt % of a polymer component having an elution temperature belowabout 40° C., determined by TREF analysis, and an average high molecularweight of greater than 90,000 g/mol, determined by GPC analysis; greaterthan 10 wt % of a polymer component having an elution temperature rangefrom about 30° C. to 60° C., determined by TREF analysis; less than 50wt % of a polymer component having an elution temperature range fromabout 60° C. to 94° C., determined by TREF analysis; greater than 25 wt% of a polymer component having an elution temperature higher than about94° C., determined by TREF analysis; a substantially constantdistribution of short chain branching across its molecular weightdistribution (MWD) in each fraction over the elution temperature rangefrom about 30° C. to 94° C., determined by GPC coupled with FourierTransform Infrared Spectroscopy Detector (GPC-FTIR); and a reverseddistribution of comonomer composition across the molecular weightdistribution in the fractions eluted over about 94° C., determined byGPC-FTIR analysis; and a high molecular weight tail in the fractionsover the elution temperature range over about 100° C.
 2. The copolymerof claim 1, wherein the alpha-olefin is 1-hexene.
 3. The copolymer ofclaim 1, wherein the molecular weight of the copolymer satisfies theformula: (Mw of 100° C.)/(Mw of 35° C.)=1.0 to 1.3.
 4. The copolymer ofclaim 1, wherein the copolymer has a sporadic long chain branches withJ-C α value of less than
 1. 5. The copolymer of claim 1, wherein thecopolymer has a melt strength index, defined as the ratio of storagemodulus to loss modulus (G′/G″) at a shear rate of 0.03 s-1, is lessthan
 3. 6. The copolymer of claim 1, wherein the copolymer has a ratio(Mz/Mw) of z-average molecular weight (Mz) to average weight molecularweight (Mw) of between 3.2 and 4.5.
 7. The copolymer of claim 1, whereinthe molecular weight (Mw) of the fractions eluted over about 100° C. ishigher than 200,000 g/mol.
 8. The copolymer of claim 1, wherein thefractions eluted over about 100° C. is at least 5 wt % of acrystallizing polymer component.
 9. The copolymer of claim 1, whereinthe copolymer is prepared by copolymerizing ethylene with one or morehigher alpha-olefin comonomers in the presence of a Ziegler-Nattacatalyst system comprising: a catalyst precursor comprising Ti, Mg, Si,halogen, and nitrogen; and a cocatalyst selected from containinghalogenated aluminum alkyl or organohalogenous aluminum compounds. 10.The copolymer of claim 9, wherein the catalyst precursor is prepared bycontacting a magnesium-based composite support with an organic siliconcomplex, a transition metal compound, a transition metal halidecompound, a substituted aromatic compound containing nitrogen, and analkyl halide or aromatic halide.
 11. The copolymer of claim 10, whereinthe magnesium-based composite support is prepared by contacting metallicmagnesium with an alkyl halide or aromatic halide in the presence of anorganic silicon compound having the formula R1mSi(OR2)n, wherein R1 andR2 are C1-C20 hydrocarbyl, m=0-3, n=1-4, and m+n=4, and wherein each R1and each R2 may be the same or different.
 12. The copolymer of claim 11,wherein the organic silicon complex is prepared by reacting analkoxysilane ester with a halogen-substituted silane.
 13. The copolymerof claim 12, wherein the alkoxysilane ester has the formula R2mSi(OR3)n,wherein R2 and R3 are independently selected from any C1-C20hydrocarbyl, m is 0-3, n is 1-4, and m+n=4.
 14. The copolymer of claim12, wherein the halogen-substituted silane has the formula R3xSiXy,wherein R3 is C1-C20 hydrocarbyl, X is halogen, x=0-3, y=1-4, and x+y=4,and wherein each X and each R3 may be the same or different.
 15. Thecopolymer of claim 10, wherein the transition metal compound has theformula M(OR4)aX4-a, wherein M is an early transition metal, wherein R4is C1-C20 hydrocarbyl, X is a halogen, and 0≤a≤4.
 16. The copolymer ofclaim 15, wherein the early transition metal is titanium.
 17. Thecopolymer of claim 10, wherein the transition metal halide compoundhaving the formula MX4, wherein M is an early transition metal, and X isa halogen.
 18. The copolymer of claim 17, wherein the early transitionmetal is titanium.
 19. The copolymer of claim 10, wherein thesubstituted aromatic compound containing nitrogen is selected from2,6-dimethylpyridine, 8-quinolinol, and 2-methyl-8-quinolinol.
 20. Thecopolymer of claim 10, wherein the alkyl halide or aromatic halide hasthe formula R5X, wherein R5 is C1-C20 hydrocarbyl.
 21. The copolymer ofclaim 9, wherein the cocatalyst is a combination of alkyl aluminum oralkylaluminoxane and halogenated aluminum alkyl.
 22. The copolymer ofclaim 21, wherein the alkyl aluminum is triethyl aluminum.
 23. Thecopolymer of claim 21, wherein the alkylaluminoxane is selected frommethylalumoxane, modified methylalumoxane, tetraethyldialumoxane,tetrabutylalumoxane, bis(diisobutylaluminum) oxide, ethylalumoxane,isobutylalumoxane, polymethylalumoxane, and mixtures or combinationsthereof.
 24. The copolymer of claim 21, wherein the halogenated aluminumalkyl is selected from dimethylaluminum chloride, diethylaluminumhalides, such as dimethylaluminum chloride, diethylaluminum chloride,diisobutylaluminum chloride, di(t-butyl)aluminum chloride,diamylaluminum chloride, methylaluminum dichloride, ethylaluminumdichloride, isobutylaluminum dichloride, isobutylaluminum dichloride,ethylaluminium sesquichloride, t-butylaluminum dichloride andamylaluminum dichloride, and mixtures or combinations thereof.
 25. Thecopolymer of claim 1, wherein the copolymer is prepared bycopolymerizing ethylene with one or more higher alpha-olefin comonomersin the presence of a prepolymer and hydrogen without using additionalco-catalyst.
 26. The copolymer of claim 25, wherein the prepolymer isprepared with (co)polymerization of ethylene or alpha olefins in thepresence of Ziegler-Natta catalyst system, comprising: a Ziegler-Nattacatalyst, which is prepared by prepared by contacting a magnesium-basedcomposite support with an organic silicon complex, a transition metalcompound, a transition metal halide compound, a substituted aromaticcompound containing nitrogen, and an alkyl halide or aromatic halide;and a cocatalyst, a halogenated aluminium alkyl and/or anorganohalogenous aluminum compound obtained in-situ by reacting alkylaluminium or alkylaluminoxane with halogenated alkylaluminum compounds.27. The copolymer of claim 26, wherein the prepolymer has a polymeramount ranging from 0.1 to 1000 g per g of the said solid catalystprecursor.
 28. The copolymer of claim 26, wherein the prepolymer ischaracterized by its sporadic long chain branches in the high molecularweight fractions with a J-C α value of less than about
 5. 29. Thecopolymer of claim 26, wherein the prepolymer has an average particlesize range from about 10 to about 500 micron, and a bulk density ofbetween about 0.28 and 0.45.
 30. The copolymer of claim 26, wherein theprepolymer has an Al/Ti ratio of from about 1.5 to
 10. 31. The copolymerof claim 1, wherein the copolymer can be used to produce a blown filmhaving a thickness of 1 mil (25 μm); a haze, determined by ASTM D-1003,ranging from about 6 to 15; a gloss, determined by ASTM D-2457, rangingfrom about 80-100; dart impart, determined by ASTM D-1709, ranging fromabout 450 to 800; and MD tear strength, determined by ASTM D-1922,ranging from about 400 to 600.